CHAPTER XXXII. 419 



pyridine to be repeatedly changed, the vessel with the pieces being kept 

 at 36 to 37 C. After washing for two to three hours in running tap 

 water, he continues as in Donaggio's method III. 



For the criticism of JADERHOLM, see Arch. mikr. Anat., Ixvii, 1906, 

 p. 108 ; and for that of MONTANARI, Ztschr. wiss. Mikr., xxviii, 1911, 

 p. 22. 



837. RAMON Y CAJAL'S Methods. Introductory. It has been said 

 by some authors that CajaPs methods were originally only modifica- 

 tions of the photographic process of Simarro. The criticism is 

 unjust because even the first formula of Cajal differs so profoundly 

 from Simarro's process as to form an entirely new method. One 

 cannot, however, deny the existence of a certain similarity of con- 

 ception between the two processes in so far as both are based on the 

 silver-reducing power of certain photographic reagents. For this 

 reason it has been thought expedient to briefly describe here Simarro's 

 process, which though uncertain in its results, may still be of some 

 value to elucidate certain histological questions. 



SIMARRO'S Process (Rev. Trim. Micr., v, 1900, p. 45) consisted in 

 poisoning animals with subcutaneous injections of solutions of 

 sodium or potassium bromide or iodide in order to impregnate their 

 living nervous tissues with one or the other of these salts. As soon 

 as the animals showed that the poisoning had reached its maximum 

 they were killed and their central nervous system removed in the 

 photographic dark room. Small pieces were then immersed in a 

 solution of silver nitrate, which, by combining with the bromine or 

 iodine with which the tissues were impregnated, gave rise to the 

 formation of silver bromide or iodide, which is easily affected by 

 light. Sections were then made (always in the dark room), best by 

 means of a freezing microtome, and exposed for a little while to light. 

 There remained only treating them with a photographic developer, 

 such as hydroquinone, pyrogallol or the like, and fixing them with 

 sodium hyposulphite and so on, as if they were photographic plates ; 

 they were lastly washed, dehydrated and mounted in the usual way. 



One can easily understand the many drawbacks of such a method 

 and the reason for which it was abandoned as soon as Cajal published 

 in 1903 his first reduced silver methods. From that time onwards, 

 Ramon y Cajal continued improving them and adding new formulae, 

 which he himself summarised in a special article of his Trab. Lab. 

 Invest. BioL, Madrid, viii, 1910, on which the following account is 

 based. The numbering is that of Ramon y Cajal. 



Formula la. Small pieces of fresh tissue are directly put into 

 1-5 per cent, silver nitrate and kept therein for three to four and 



272 



